Temperature control apparatus



M. R. MILLER Filed April 22, 1949 TEMPERATURE CONTROL APPARATUS Sept. 16, 1952 INVENTOR M. R. M/z L51? A Tron/v55) Patented Sept. 16, 1952 TEMPERATURE CONTROL APPARATUS Merton R. Miller, Lombard, 111., assignor to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York Application April 22, 1949, Serial No. 89,102

10 Claims.

This invention relates to control apparatus and more particularly to a device for automatically maintaining a heated element at a substantially constant temperature by controlling the source of heat to the element.

It is an object of the invention to provide a control device wherein the maximum and minimum temperature deviations may be adjusted independently in order to give a minimum temperature deviation in the thermal system being controlled.

In accordance with one embodiment of the invention, a control circuit is provided which is designed to control the temperature of a heated element such, for example, as a soldering iron tip. A thermocouple is associated with the heating element of the soldering iron tip in such a manner that the thermocouple E. M. F. is balanced against one of two separate D. C. potentials, depending on whether the heated element is approaching its maximum or minimum temperature. A relay system is associated with the thermocouple and the heating element in such a manner that an unbalance in the thermocouple circuit initiates various switching arrangements in the relay system to restore balanced conditions by controlling the current to the heating element. The relay system also determines automatically which of the two D. C. potentials the thermocouple E. M. F. is balanced against, depending on the direction of the temperature swing as controlled by the heating element at that particular time.

A complete understanding of the invention will be had by referring to the following detailed description taken in conjunction with the accompanying single figure drawing which is a diagrammatic illustration of one embodiment of the invention.

In this control circuit, there is provided a pair of direct current energized potentiometers l and H having movable contacts !2 and I3, respectively, which contacts may be set to determine the temperature at which heating current will be supplied to and cut off from a heating element M. The heating element I4 may be connected to a suitable source of current such, for example, as an alternating current source l5 by a control circuit which operates under control of a thermocouple I6. Thermocouple l6 and heating element [4 may be mounted in an element I! such, for example; as a soldering iron tip,'the temperature of which it is desired to control; The thermocouple i6 is connected through the contacts of a relay I8 and a relay IS in such a manner that it is alternately connected to the movable contacts I2 and I3 of the potentiometers l0 and II and simultaneously connected in series with an operating coil 20 of a meter-type relay 2|, the electrical connection being such that a flow of current in the thermocouple circuit causes a pointer 23 on the metertype relay 2| to be deflected to make contact with a fixed contact 22, where the pointer 23 is held by a holding magnet 24.

Pointer 23 is connected to the positive side of a source of direct current, as shown, and its defiection to make contact with contact 22 causes a circuit to be completed through a movable contact 25 and either a fixed contact 26 or a fixed contact 21 on relay I9 to winding 28 on relay I8, which is connected to the negative side of a source of direct current, as shown, or to winding 29 of relay [9, which is also connected to the negative side of a source of direct current, as shown. A restoring coil 30 on the meter-type relay 2| has one side connected to the negative side of a direct current source, as shown, and has its other side connected through a movable contact 3| and a fixed contact 32 of the relay I8 and a fixed contact 33 and a movable contact 34 of relay l9 to the positive side of a direct current source, as shown. Restoring coil 30 is also connected through a movable contact 35 and a fixed contact 36 of relay l 8 and a fixed contact 3'! and a movable contact 38 of relay 19 to the positive side of a source of direct current potential, as shown. Thus it will be obvious that the restoring coil 30 may be operated to restore the pointer 23 by one of two circuits, depending on the position of the contacts of the relays l8 and I9.

Relay I8 is also provided with contacts 39, 4O, 41, 42, 43 and 44, the function of which is to reverse the connections to operating coil 20 when the connection from the thermocouple I6 is transferred from one of the movable contacts l2 and 13 of the potentiometers l0 and H to the other of the movable contacts, this reversal of connections being necessary because of the reversal of the direction of current flow in the thermocouple circuit when the thermocouple connection to the movable contact of one potentiometer is broken and connection to the movable contact of the other potentiometer is made, it being noted that in the case of a decreased temperature, the potential across the appropriate potentiometer will cause the current flow, and in case of an increased temperature, the increased potential of the thermocouple will cause the current flow, and. these flows will be in opposite directions.

Connection from the thermocouple It to the appropriate movable contact of the potentiometers is provided through contacts 45, do and 4? of relay 19, contact at being movable between the contacts 45 and 6?, which are stationary. Relays I8 and J9 arelcapable of being locked operated in series, :for reasons which will more fully appear in the description of the operation of the circuit. To provide suitable connections for locking the relays I8 and I9 operated, the Winding'28 onrelay I8 may be connected through a pair of contacts 48, 43 on relay I8 to a winding on relay I9, the winding '56 being connected to the positive side of a source of direct current, as shown. Thus it is obvious that under .certain conditions the windings 28 and 5b may be energized in series, thus operating both relays, and since the only contacts which may break this circuit are the contacts "#8, 4 9. which are held closed by the operation of relay 428, 'itis obvious that some additional .means must be provided to cause the relay 18 to release. For this purpose, a winding 1 :is provided on relay 18, the windingti having one side connected to the negative side of a source of direct current, as shown. The circuit to winding 5| is completed through apairiqfcontacts :52, 53 on relay I8, contacts 2-7, on relay I9, contact 22 of the meter-type relay 2!, and

pointer ,28 to the source of positive direct current connected to the pointer 23. Therefore, it will he seen that deflection oi the pointer 23 to make contact with the contact 22 at a time when the contacts 25, Hand '52 53 are closed will cause energization of winding -5 -I in magnetic opposition .to winding 28, thereby causing relayls to release. 7

All of the operations of the circuit described .hereinbefore are so coordinated as to control the opening and closing of a pair of contacts tid, on relay 1-9 to control theflow of current to the heating element L4,, and it will be observed that .a neon glow tube 5.5, which has one side connected to the negative side of a source of direct current, as shown, may also be provided to give -.a visual indication that the contacts .54, 55 are closed, the other side of the neon indicator 55 :being connected through contacts .38 .to the ,Positiveside of a source of direct current whenever the relayl 9 operates to close -.con,tacts .54 55.

.In the operation of ,the device, assuming .a ,point in the operation where the current .to the heating element I4 is turned off, the contacts of relays l8 and ,IS- will be positioned as shown in the drawing. E. M. F. is decreasing as the element cools and is being opposed by the potential which was pres .setuon potentiometer lb. As the thermocouple E. M. vF. decreases below the value .set on the potentiometer It), the current through the operating coil 26 of the meter-type relay 2..I causes the pointer '23 to be deflected away from its back stop and to make contact with the contact 22, where it is held by the action of the holding .magnet 25. Closure of the contacts of the meter-type relay ,2I causes the winding 28 of relay is to be energized 'througha .circuit from positive potential through .pointerid, fixed contact I22, relay contacts Ziand 25, through the Winding .28 to negative, thus operating relay 18. Operation of .relay .I8 extends positive potential ,from the closed contacts of the meter-type relay 2] to the winding 5.8 of relay t9; however, relay 1.9 does not operate at this time because the At this time, the thermocouple other side of its winding 50 is also connected to positive potential. The operation of relay 8 also reverses the operating coil 2% of the meter-type relay 2| at contacts 35, 43, ll, 42, 43 and 44 and extends positive potential from the normally closed contacts 33 and 34 through contacts 3| and 32 to the restoring coil Operation of the restoring coil (it removes the positive potential from the winding 28 of-relay I3, thereby causing relay I9 to operate by virtue of the circuit from positive potential on the winding 53 through the winding .28 to negative potential; thus, relays I8 and I9 are locked operated in series. The operating of relay is closes contacts 54, E5 to extend power to the heating element It and extends positive potential through its contacts 31 and $8 to indicator tube 5%, thereby causing the tube '56 to light. At the same time, the operatio'nof relay id transfers the thermocouple balancing circuit from the potentiometer It? to the potentiometer ii at contacts .55, iii}. landll, transfers the. meter-type relay contactcireuit from the primary winding of relay I3 to-the primary winding of relay re at contacts-25.2. and 2?, and breaks the circuit to the restorin coil fillet contactstB and 34. v

t this point in the operation, whei-ithe power to the heating element is has been turned on, as described above, relays i8 and L5 are locked operated in series'and the thermocouple E. M. is increasing as the element It heats; however, no action occurs until the thermocouple M. F. rises to .a value exceeding the-potential across potentiometer 1H,. .coupleE. M. F. .exceedsthe value ojthe po across potentiometer II by predetermined amount, the pointer again moves to the right, closing the contacts of the meter-type relay 2I. This action extends positive potential from the pointer 23 through the fixed contact 2.2, relay contacts 2-? and .25, and relay contacts .512 and 5?. to the winding 5%. Since the winding o-Iv is connected in opposition to the winding 2 8, energization of the winding iii in magnetic opposittion to winding 2.8 will cause relay {-8 to release. The releasing of relay 48 opens the series connection between its winding 28 andthe winding 5: of relay 1 9 at contacts 48 and as; how ever, the relay 13 does not release 'at -this --,ti-me because it is locked operated by its winding 29 through contacts Z i'and Ed -to the pointer 23 of the meten-t-ype -relay. The releasing of relay I8 also opens the circuit :to its winding o l at contacts 52 and 53, reverses theoperating coil 2i at contacts 39, Ail, AI, 132, 43 and it, and ex== tends positive potential from contacts .36 and 3-? through its own contacts 36 and-35 to'operate the restoring coil 30. *Operation'of the restoring coil 38 retracts the pointerZS, therebyiremcving the positive potential from the contacts 25 and 2I-and .the winding 23-, thus causing relay I9 to release. The releasing Of' relay 19 opens the circuit to the restoring coil 39 and to the neon lamp at contacts 3? and so, transfers the thermocouple balancing circuit from poten tioi'neter I l to potentiometer iii 'at'contacts d5, 45 and ti, and opens the contacts '51; and .55 to pen the circuit to the heating elementjo under control. r

The control circuit described herein has been described in conjunction with an electrically heated element; however, it is towbe understood that the principles of operation would not ,be changed if other types of heating medium were employed. For example, the relay J9 maybe-doe signed to control a valve insteadoff contacts '54, 55, therebyto control-the flow of a liquid or gas eous heating-medium to heat an element It is'to be understood'that the above-described arrangements are simply illustrative of the application'of the principles of the'invention. Numerous other arrangements may be readily devisedby those skilled in the art which will embody the principles of the invention and fall within the spirit and scope thereof.

What is claimed is:

J 11. In a temperaturecontrol device wherein an elementis heated by an electrical current, the combination with a thermocouple. responsive to the temperature'of said element to producea di rect. current proportional thereto, of a pairof separately adjustable direct current energized potentiometers alternately connectible in series circuit with said thermocouple to provide a current in opposition to the current produced by said thermocouple, means connecting one of said potentiometers in said circuit, means responsive to a flow of current in said circuit caused by an increased temperature of said element to stopv the flow of heating current to said element and simultaneously disconnect said one potentiometer from said circuit and substitute the other potentiometer therefor, and means responsive thereafter to a flow of current in said circuit in an opposite direction caused by a decreased temperature of said element to start the flow of. heating current to said element and simultaneously disconnect said other potentiometer and connect said one potentiometer in place thereof.

2. In a temperature control device in combination, a heating element energizable by a source of heating current, a heated element, a thermocouple responsive to the temperature of said heated element to produce a direct current proportional thereto, a meter-type relay having its deflecting coil connected in series with said thermocouple, a pair of direct current energized separately adjustable potentiometers alternately connectible in series with said thermocouple and said meter-type relay deflecting coil, means connecting one of said potentiometers in series with said thermocouple and said deflecting coil whereby the current flowing across said potentiometer opposes the current generated by said thermocouple, a pair of direct current relays energizable by the deflection of a pointer on said meter-type relay, said deflection being initiated by a flow 01' current through said deflecting coil, and switch means responsive to a flow of current in said pair of relays to control the flow of current to said heating element, remove said one potentiometer from said thermocouple-deflecting coil circuit and substitute the other potentiometer therefor, and reverse the electrical connections to said deflecti-ng coil.

3. In a device for controlling the flow of current to a heating element, the combination with a thermocouple, of a pair of variable resistances, a source of potential across said resistances, relay means alternately connecting said resistances in series with said thermocouple and simultaneously controlling said flow of heating current, and means responsive to a predetermined thermocouple temperature change to actuate said relay means.

4. A device for controlling the temperature of a heated element comprising a heating element, a source of current for said heating element, switch means for controlling the current to the heating element, a thermocouple, first means connected 6 to said thermocouple fol-opposing the F. of the thermocouple, second means for separately opposing the E. M. F.- of the thermocouple,'relay means responsive to a condition of unbalanced E. M. F. between the thermocouple and said first opposing means for controlling said switch means and for simultaneously disconnecting said one opposing means from the thermocouple, and sub stituting said second opposing means therefor.

5. In a temperature control device wherein an element is heated by a heating means, the combination with a thermocouple responsive to the temperature of said element to produce a direct current proportional thereto of a pairof separately adjustable direct current energized potentiometers alternately connectible in series cirsuit with said thermocouple to provide a current in opposition to the current produced by said thermocouple,means connecting one of said potentiometers in said circuit, means responsive to a'flow of current in said circuit caused by anincreased temperature of said element to render the heating means for the heated element inoperative and simultaneously disconnect said one potentiometer from said circuit and substitute the other potentiometer therefor, and means responsive thereafter to a flow of current in said circuit in an opposite direction caused by a decreased temperature of said element to render the heating means for said element operative and simultaneously disconnect said other potentiometer and connect said one potentiometer in place thereof.

6. In a temperature control device in combination, an element heated by a supply of heating medium, a thermocouple responsive to the temperature of said heated element to produce a direct current proportional thereto, a meter type relay having its deflecting coil connected in series with said thermocouple, a pair of direct current energized separately adjustable potentiometers alternately connectible in series with said thermocouple and said meter type relay deflecting coil, means connecting one of said potentiometers in series with said thermocouple and said deflecting coil whereby the current flowing across said potentiometer opposes the current generated by said thermocouple, a pair of direct curent relays energizable by the deflection of a pointer on said meter type relay, said deflection being initiated by a flow of current through said deflecting coil, and means responsive to a flow of current in said pair of relays to control the flow of heating medium to said element, remove said one potentiometer from said thermocouple deflecting coil circuit and substitute the other potentiometer therefor and reverse the electrical connection to said deflecting coil.

7. In a device for controlling the flow of heating medium to a heated object, the combination with a thermocouple of a pair of variable resistances, a source of potential across said resistances, relay means alternately connecting said resistances in series with said thermocouple and simultaneously controlling said flow of heating medium, and means responsive to a predetermined thermocouple temperature change to actuate said relay means.

8. A current responsive temperature control circuit comprising a heating element, a source of heating medium for heating said element, a thermocouple, a first resistance, a second resistance, a source of direct current connected across each of said resistances, means connecting said resistances alternately in series circuit with said 9=. Ina temperaturecontrol device-wherein an element is heated by an. electrical current, the

combination of a source of potential, a thermocouple responsiveto temperature of said element to produce an E. proportional tothe temperature,- a starting resistance, a stopping resistance, a source of D. 0'. potential connected to. the resistances, relay means operable upon one actuationv thereof for. connecting the thermocouple in series with one of said resistancesand the.- element. to saidfirst source'of potential and operable upon. alternate actuations thereof I for connecting, the thermocouple to the other resistance anddisconnecting the said element from said :first-source. of current, and sensitive relay means responsive to the F. of the thermo couple for actuating, the relay meanswhenlthe thermocouple. is at a predetermined maximum temperature and for actuating the relay means when the thermocouple is at a predetermined minimum temperature. I

10. In a temperature control device wherein an element is heated by an electrical current, the combination of a source of potential, a thermocouple responsiveto the temperature of said ele- 'ment to produce an E. M. F. proportional to the temperature thereof, a starting resistance, a stopping resistance, means for supplying said eleelementand disconnecting said sourceirom. said element. or I .jIVIERTQNRLMILLERL,

REFERENCES CITED The following references are of record in; the

file of this patent:

' UNITED STATES PATENTS Number Name Date 1,815,061 I-Iarsch et a1. July 21, 1931 2,046,850 Wilhjelm July 7, 1936 2,085,855 Hunt July 6, 1937 2,085,856 Hunt et a1. July 6, 1937 2,139,504 King Dec. 6, 1938 2,148,491 Moore Feb. 28,1939 2,220,028 Smith Oct. 29, 1940 Jones May 22, 1945 

